Highly efficient luminescent hybrid materials covalently linking with europium(iii) complexes via a novel fluorinated β-diketonate ligand: synthesis, characterization and photophysical properties

Abstract

A novel highly fluorinated β-diketonate ligand, 1-(3,5-bis(benzyloxy)phenyl)-4,4,5,5,5-pentafluoropentane-1,3-dione (HBBPPF) and its corresponding europium(III) ternary complex, Eu(BBPPF)₃(DDXPO) [DDXPO = 4,5-bis(diphenylphosphino)-9,9-dimethylxanthene oxide] were synthesized via a dexterously designed routine, characterized and its photophysical properties (PL) investigated. PL measurement results indicated that the europium(III) ternary complex exhibits intense red emission under UV light excitation with a solid-state quantum yield of 39%. An organic–inorganic mesoporous luminescent hybrid material was also constructed by linking the ternary europium(III) complex to the functionalized hexagonal mesoporous MCM-41 through the modified β-diketonate ligand (SiBBPPF-Na). β-Diketonate grafted to the coupling agent 3-(triethoxysilyl)propyl isocyanate was used as the precursor for the preparation of mesoporous materials. A modified MCM-41 mesoporous material containing ternary europium(III) complex covalently bonded to the silica-based network, designated as Eu(BBPPF-Si)₃(DDXPO)/MCM-41, was obtained by interacting SiBBPPF-Na with europium nitrate, DDXPO and MCM-41 via a ligand-exchange reaction. The new mesoporous hybrid material was characterized by powder X-ray diffraction, nitrogen adsorption–desorption, thermogravimetry, transmission electron microscopy, dynamic light scattering, FT-IR, ²⁹Si CP MAS NMR and ¹³C NMR solid-state techniques, and photoluminescence spectroscopy. Eu(BBPPF-Si)₃(DDXPO)/MCM-41 exhibits an efficient intramolecular energy transfer process from the silylated β-diketonate to the central Eu³⁺, namely, the “antenna effect”, which favours a strong luminescent intensity (quantum yield = 43%). Thermogravimetric analysis on Eu(BBPPF-Si)₃(DDXPO)/MCM-41 demonstrated that the thermal stability of the lanthanide complex was evidently improved as it was covalently bonded to the mesoporous MCM-41 matrix.